Process for the catalytic hydrogenation of aromatic hydrocarbons



Aug 24,

HYDROGEN 6 QwuMP c. THONON 3,202,723 PROCESS FOR THE CATALYTICHYDROGENATION OF AROMA'IIC HYDROCARBONS Filed Sept. 15, 1962 J 24 I LLHYDROGEN RECYCLE H 5 SECOND REACTION ZONE 5 5 cowoamszn 5 15 16SEPARATING UNIT 14 9PUMP 4 CYCLOALIPHATIC HYDROCARBON FIRST REACTIONZONE HEAT EXCHANGER PUMP AROMATIC HYDROCARBON INVENTOR CLEMENT THONO/VATTORNEY$ 3,202,723 PROCESS FOR THE CATALYTIC HYDROGENA- TRON F AROMATICRQCARBONS Clement Thonon, Seine-et-Oise, France, assignor to InvstitutFrancais (in Petrole des 'Carhurants et Lubrifiants,

Rueil-Malmaison,Seine-et-Oise, France Filed Sept. 13, 1962, Ser. No.223,393 Qlaims priority, applicatiorgrance, Sept. 13,1961,

9 Claims. hi. 260-667) version is conducted with the starting materialin the vapor phase. These known processes, however, suffer from variousdisadvantages, particularly if it is desired to produce a cycloaliphatichydrocarbon of a high purity as presently required for industrial uses.

The vapor phase processes yield an undesirably low output per unitvolume of reaction zone. This is due not only to the low density of thetreated product but also to the difficulties encountered in attemptingto cool said reaction zone efiiciently. It is necessary either to use abulky apparatus comprising critical and costly internal cooling circuitsso as to completely avoid local overheating of the catalyst which ifuncontrolled would result in a reduction of catalyst activity; or, onthe other hand, to dilute the aromatic hydrocarbons in a large volume ofgases or vapors, for instance, in the corresponding hydrogenatedproducts, which requires the recycling of a large portion of the latterand accordingly leads to a poor hourly rate of production of the plant.

Considering now the liquid phase processes, particularly those in whichthe aromatic hydrocarbons, together with hydrogen, are introduced into asuspension of the catalyst in a large excess of the correspondingcycloaliphatic hydrocarbon, it is to be noted that although thesesystems provide for an eiiicient removal of the heat produced by thereaction (particularly when the hydrogenated hydrocarbon is removed bydistillation) these systems are far from entirely satisfactory,primarily because are products obtained thereby are not of asufficiently high purity. As a matter of fact, it is not technologicallypractical during such a distillation, to completely separate treatedhydrocarbon from the hydrogenated product, as these two products havevery close boiling temperatures. Furthermore, if an etiort is made toconvert substantiallyall the aromatic hydrocarbon in the reaction zone,the rate of reaction is substantially decreased under these conditions.

Accordingly, the liquid phase processes are not easily applicable whenit is desired to get a large output of cycloaliphatic hydrocarbons of ahigh purity, since such a result is only achieved by use of either of avery bulky apparatus or of a series of reaction vessels of substantiallyequal volumes in the first of which the major part (for instance 95%) ofthe aromatic hydrocarbon is converted, whereas in the other reactionvessels the conversion is limited to decreasing portions of the aromatichydrocarbons (for instance 3.5% in a second reaction vessel, 1% in athird one, 0.3% in a fourth one, etc.), the cycloaliphatic hydrocarbonproduced being eventua United States Patent reaction.

ally separated from the reaction product obtained at the outlet of eachof the successive reaction vessels, by dis tillation. Such a processrequires the use of a very large and expensive equipment as well as theaddition of external for carrying out the separation of thecycloaliphatic hydrocarbon by distillation in the last stage or stagesof As a matter of fact, in view of the low conversion rate in these laststages, the heat generated by the reaction is neglible and, therefore,insuflicient for the distillation of the reaction product. It is alsoimpossible to use the heat generated by the reaction in the precedingstages for distillation of the last stage products since the heat isproduced at too low'a temperature level.

It is, therefore, an object of this invention to provide for theconverison of aromatic hydrocarbons, such as, for instance, benezene,toluene and/or xylene, to the corresponding cycloaliphatic hydrocarbons,under such conditions as to obtain the latter with a high degree ofpurity.

It is another object of this invention to carry out said conversion witha suifieient reaction rate per unit volume of the reaction zone.

It is yet another object of this invention to avoid the use of extensiveand expensive cooling means in the reaction zone and/or localoverheating of the catalyst.

It is still another object of this invention ,to carry out theconversion of aromatic hydrocarbons to the corresponding cycloaliphatichydrocarbons without dilution of said aromatic hydrocarbons in the vaporphase with a large volume of gases or vapors which have to be recycled.

It is a further object of this invention to carry out catalytichydrogenation of aromatic hydrocarbons with high conversion rates at asatisfactory reaction velocity.

It is still a further object of this invention to provide for theconversion of aromatic hydrocarbons to the corresponding cycloaliphatichydrocarbons without use of substantial amounts of external heat.

These and other objects as may be apparent from a study of the followingspecification and claims, are achieved by the process of this inventionas follows:

(1) The aromatic hydrocarbon is introduced together with hydrogen inexcess or in amount at least a stoichiometric ratio, in a first reactionzone containing the corresponding cycloaliphatic hydrocarbon in theliquid phase having suspended therein a catalyst for liquid phasehydrogenation, the molar ratio of said aromatic hydrocarbon to thecorresponding cycloaliphatic hydrocarbon being maintained at asubstantially constant value comprised between 0.003 and 0.1; and,

(2) The gaseous flow issuing from the bath is then caused to passthrough a second reaction zone containing a solid catalyst forhydrogenation in the gaseous phase, the outlet gaseous flow issuing fromsaid second reaction zone consisting of excess hydrogen and thecycloaliphatic hydrocarbon of high purity which may then be condensed bycooling.

. The attached drawing depicts in fiowsheet form, an embodiment of thisinvention.

Under the conditions of this invention, a cycloaliphatic hydrocarbon ofhigh purity is obtained with a high output rate. Furthermore, the heatnecessary for vaporizing the hydrocarbons in view of their treatment inthe second reaction zone, is only that heat generated by the reactionconducted in the first reaction zone, so that any addition of externalheat may be avoided.

The molar ratio between the aromatic hydrocarbon and the cycloaliphatichydrocarbon may be easily determined by conventional means, forinstance, by ultraviolet spectrography and gas chromatography. In thefirst reaction zone, the molar ratio of aromatic to cycloaliphatichydrocarbons is 0.003-0.l:l, preferably (LOGS-0.05:1

Patented Aug. 24, 1965 respectively. The intermediate product streamwhich is fed to the gas phase reaction zone generally contains thearomatic to cycloaliphatic hydrocarbons in a molar ratio of about0.003-0.1:1, preferably 0005-005: 1, respectively.

The catalysts used in each of the two stages of reaction areconventional hydrogenation catalysts. The catalyst in the first reactionzone is a solid conventional catalyst for liquid phase hydrogenation,and it is suspended in the liquid hydrocarbon. In the second reactionzone, a conventional catalyst for gaseous phase hydrogenation may beused in the form of a stationary, a moving or a fluid bed, thestationary bed being, however, preferred. These catalysts may be usedeither as such, or deposited on any carrier.

By way of example, there may be used as a catalyst, a metal of the 8thgroup of Mendeleefis periodic table; particularly nickel, cobalt,platinum, palladium, rhodium, or ruthenium, and as a support there maybe used alumina, silica, pumice stone, asbestos, clays and the like.

The reaction temperature and pressure are selected in the range of thetemperatures and pressures commonly used when operating with thepreviously mentioned hydrogenation catalysts, and at such a level withinsaid range as to maintain a liquid phase during the first step of theprocess and a gaseous phase during the second step.

In the first reaction zone the operating temperature will preferably beabout 10 C. to 100 C., preferably about 30 C. to 70 C. below the actualboiling temperature of the cycloaliphatic hydrocarbon under theprevailing total pressure. By way of example, satisfactory reactionvelocities for an industrial plant may be obtained at temperaturesbetween 80 and 250 C. and under pressures in the range of from 1 to 100atmospheres, these limits being not, however, strictly obligatory. Thetemperature and pressure used for the first step may be difierent fromthose selected for conducting the second step.

The two steps may be, if desired, conducted under substantially the sametemperature and pressure conditions, provided that the partial pressureof the hydrocarbons in the outflow of the first stage he reduced, forinstance by dilution of the same with hydrogen or recycled gas so as toavoid any undesirable condensation of the hydrocarbons during the secondstage of the reaction. Alternatively, condensation may be prevented byoperating the second reaction zone at a lower pressure or highertemperature than the first zone.

The amount of hydrogen used is at least equal to the stoichiometricproportion corresponding to the desired degree of saturation, forinstance 3 mols of hydrogen per mol of benzene, toluene or xylene and 2or 5 mols of hydrogen per mol of naphthalene, etc. An excess of 100% ispreferred. Hydrogen may be used either in pure form or in admixture withother diluent gases such as, for instance, methane, or nitrogen.Furthermore, it is of advantage to recycle the excess hydrogen separatedfrom the outflow of the second reaction zone, said hydrogen streamcontaining significant proportions of such diluent gases.

This invention will be further explained in more detail with referenceto the accompanying drawing showing a fiowsheet of a preferredembodiment of the present invention.

The schematically illustrated apparatus comprises essentially, a firstreactor 1 wherein is conducted the first hydrogenation step, a heatexchanger 2, a second reactor 3, a condenser 4, a separating unit 5 forseparation of incondensable gases from the liquid product, and pumpmeans 6, 7, 8 and 9.

The reaction vessel 1 containing the cycloaliphatic hydrocarbon havingthe catalyst suspended therein, is fed with the corresponding aromatichydrocarbon through the pipe 10, the circulating pump 7, and the pipe11. Hydrogen is conveyed through pipe 12, the circulating benzene.

At the outlet of said condenser the outflow is partially condensed andcaused to pass through pipe 17 to the separating unit 5 from where thepure liquid cycloaliphatic hydrocarbon is removed through pipe 18whereas the incondensable gases are recycled to the input of the firstreaction vessel through pipe 19.

A part of the reaction mixture contained in the reaction vessel 1 iscontinuously withdrawn through pipe 20, passes through the pump 8, thepipe 21 and the heat exchanger 2 and is recycled to the reaction vessel1 so as to maintain the temperature therein substantially constant. Itis to be appreciated, however, that other circulation systems forremoval of heat may be used such as thermo-siphon cooling, heat exchangemeans internal to the reaction vessel Or the like.

According to another embodiment of apparatus for carrying out theprocess of the invention, the reaction vessel 3 may be juxtaposed to theupper part of the reaction vessel 1.

Various modifications may be made to the immediately describe-d system.Thus, for instance, a portion of the gases recycled through pipe 19 maybe conveyed through pipe 23 to the reaction vessel 3, said gasesconstituting a diluent which prevents any undesirable condensation ofhydrocarbon vapors in the reaction vessel 3. Another improvementconsists of withdrawing from the pipe 24 a part of the recycled gases soas to avoid any excessive accumulation of inert gases such as CH CO, Nand the like.

Alternatively, another embodiment which is not shown may consist ofliquefying a portion of the recycled gases so as to separate therefromthe inert gases which are more easily liquefiable than hydrogen.Obviously, other design and engineering changes may be made by thoseskilled in the art without departing from the essence'of the invention.To demonstrate the technological progress and unobviousness of thepresent invention, the following comparative examples illustrate theadvantages of the present process (Examples 1, 6 and 7) as compared tothe prior art processes (Examples 25).

Example 1 A conversion is conducted in an apparatus corresponding to thefiowsheet of FIGURE 1, at a temperature of 200 C. and under a. pressureof 40 kg./cm. in both reaction vessels 1 and 3.

Forty-five kg. of cyclohexane are introduced together with 5 kg. ofdivided Raney nickel into the reaction vessel 1 which is thereafter fedwith benzene at a rate of kg./hour and with hydrogen in 30 %excess ofthe stoichiometric ratio. Under these conditions, the reaction volume iskept constant, with a molar ratio benzene/cyclo hexene in the liquid andgaseous phases of about 0.015. The gaseous outflow from reaction vessel1 is then passed through the reaction vessel 3 containing 2.5 kg. of acatalyst consisting of activated carbon having a 20% nickel contentdeposited thereon, said catalyst being used in the form of a stationarybed.

The cyclohexane product is obtained in a substantially quantitativeyield by condensation of the effluent from the reaction vessel 3 and theproduct contains only 0.01% Furthermore, no additional heat is requiredduring the reaction.

Example 2 'the liquid phase in a single reaction vessel 1. It is thus1500% increase in the undesired impurity.

Example 3 Example 2 is repeated with a reaction'mass consisting of 20kg. of R-aney nickel and 180 kg. of cyclohexane. Under these conditions,the cyclohexane obtained as reaction product still contains 0.12%benzene, which is equivalent to a 230% increase in the undesiredimpurity.

' Example 4 Example 1 is repeated except that 'thereaction vessel 3 isreplaced by another reaction vessel for liquid phase operation which isidentical to the reaction vessel 1, each of the two reaction vesselsinitially containing- 5 kg. of Raney nickel and 45 kg. of cyclohexane.

Under these conditions (two reaction vessels for liquid phase operation)the cyclohexane obtained as reaction product still contains about 0.1%benzene. Consequent- 1y, this example not only yields about a 100%increase in impurities as compared to Example 1, but it also requiresthe use of a large amount of external heat for thesecond reaction vesselso as to secure the removal of the reaction product inthe vapor phase.Thus, this example yields a less pure product as well as a moreexpensive operation.

Example 5 According to this example, there is used only one reactionvessel for operation in the vapor phase. In order to secure a conversionof 100 kg./hour of benzene, it is necessary to make use of a reactionvessel having a volume corresponding to about 20 times the volume of thereaction vessel 3 for operation in the vapor phase according to Example1, and of 50 kg. of a catalyst consisting of nickel deposited on activecarbon and used in the form of a stationary bed. It is also necessary torecycle and cool the eflluent flow from the reaction vessel at a rate of1500 kg./hour so as to remove the heat generated by the reaction. 7

Under such conditions it is impossible to maintain a constanttemperature in the reaction vessel since the temperature at the feedthereof is 160 C., whereas at the outlet the temperature is 220 C.

In addition to these drawbacks of great equipment expense and lack ofcontrol, the cyclohexane obtained as reaction product still contains a0.09% benzene content, which amounts to an 80% increase in the contentof the undesired impurity, which is of course again highly dele terious.

The preceding five examples repeated except with different hydrogenationcatalysts and/or diflerent temperatures or pressures as taughtpreviously, yield substantially the same comparative results. It is tobe emphasized that the essence of this invention resides in a liquidphase catalyst hydrogenation reaction followed immediately by a gasphase hydrogenation catalytic reaction to result in an economical andsimple process yielding highly pure cycloparaffins substantially devoidof the aromatic starting materials.

It will be understood that while there have been given herein certainspecific examples and suggestions for the practice of this invention, itis not intended thereby to have the invention limited to orcircumscribed by the specific details ofcatalyst starting materials,proportions or operating conditions herein specified, in view of thefact that the invention may be modified according to individualpreference or conditions without departing from the spirit and scope ofthis disclosure and thereby being within the range of equivalence of thefollowing appended claims.

Such modifications will be exemplified by the following non-limitativeexamples. 7 V

Example 6 Example 1 is repeated, except that there is initiallyintroduced into the reactionvessel ,1, 67.5 kg. of'cyclohexane and 75kg. of a divided catalyst consisting of 35% by weight kieselguhr and 65%by weight nickel deposited? thereon, and except that the reaction vessel3 contains. 3.5 kg. of a catalyst consisting of 15% by weight. nickeland 85% by Weight alumina, said catalyst having been previouslyactivated at a temperature of about 340". C. for 6 hours in hydrogen.

The results of Example 1 remain substantially unchanged. I

Example 7 Into an apparatus corresponding to theflowsheet of FIGURE .1,there is introduced 90 kg. of methylcyclohexane and 10 kg. of dividedRaney nickel, and then toluene at a rate of 100 kg./hour and hydrogen inexcess over the stoichiometric ratio.

The gaseous outflow is then passed through the reaction vessel. 3containing-4 kg. of .a catalyst consisting of 20% by weight nickel and80% by weight activated carbon, said catalyst being used in the form ofa stationary bed. Methylcyclohexane containing 0.03% benzene is obtainedin a substantially What is claimed is:

1. A process for the catalytic, non-destructive hydrogenation of atleast one aromatic hydrocarbon, which process comprises the steps of:

(1) introducing said aromatic hydrocarbon in the liquid state into thecorresponding liquid cycloaliphatic hydrocarbon contained in a firstreaction zone, passing through said cycloaliphatic hydrocarbon, anamount of gaseous hydrogen at least equal to the stoichiometric ratiowith respect to the aromatic hydrocarbon, said liquid cycloaliphatichydrocarbon having a Group VIII metal hydrogenation catalyst suspendedthereinto, the molar ratio between said aromatic hydrocarbon and saidcycloaliphatic hydrocarbon in said first reaction zone being maintainedwithin the range of from 0.003:l to 0.111, the pressure being comprisedbetween about 1 and 100 atmospheres and the temperature comprisedbetween and 250 C., provided the temperature is at least 10 C. lowerthan the initial boiling temperature of said cycloaliphatic hydrocarbonunder the prevailing pressure, and

(2) passing as such the whole, unreacted hydrogen and vaporizedhydrocarbons-containing gaseous phase issuing from said first reactionzone through a bed of a Group VIII metal hydrogenation catalyst in asecond reaction zone, at a temperature and a pressure in the same rangeas in the first zone, provided they are convenient to maintain saidunreacted hydrogen and vaporized hydrocarbons in the gaseous state,thereby resulting in a highly pure gaseous cycloaliphatic hydrocarbonproduct substantially devoid of any aromatic hydrocarbon impurities, and

quantitative yield.

further resulting in a process requiring neither external heat nor largeequipment normally associated with gas phase reactions.

2. The process of claim 1 wherein the temperature in the first reactionzone is from 10 to C. lower than the boiling temperature of thecycloliphatic hydrocarbon under the prevailing total pressure.

3. A process according to claim 1, wherein the molar ratio between thearomatic hydrocarbon and the corresponding cycloaliphatic hydrocarbon iskept substantially unchanged throughout the first reaction zone.

4. A process according to claim 1, wherein the temperature in the secondzone is substantially higher than in the first zone.

5. A process according to claim 1, wherein the pressure in the secondzone is substantially lower than in the first zone.

6. A process according to' claim 1, wherein the operating conditions ofpressure and temperature are substantially the same in both reactionzones.

7. A process according to claim 1, wherein the aromatic hydrocarbon isbenzene. A

8. A process according to claim 1, wherein the aromatic hydrocarbon istoluene.

9. A continuous process for the catalytic, non-destructive hydrogenationof an aromatic hydrocarbon, which process comprises the steps of:

(1) reacting hydrogen with an aromatic hydrocarbon selected from thegroup consisting of benzene, toluene, xylene, and naphthalene to producethe corresponding cycloaliphatic hydrocarbon, said reaction beingconducted in a reaction medium comprising said aromatic hydrocarbon inthe liquid phase, the correspbnding liquid cycloaliphatic hydrocarbonand a solid catalyst suspended in said liquids, said catalyst selectedfrom the group consisting of nickel, cobalt, platinum, rhodium andruthenium, the ratio of hydrogen to said aromatic hydrocarbon being atleast stoichiometric; the molar ratio of said liquid aromatichydrocarbon to said liquid cycloaliphatic hydrocarbon beingsubstantially constant and being in the range of 0.0030.1 1,respectively, the operating temperature being 80250 C., the operatingpressure being about 1-100 atmospheres, and with the pro- 3 8 visionthat said operating temperature is l0100 C. lower than the boilingtemperature of the cycloaliphatic hydrocarbon prevailing at the totalreaction pressure;

(2) withdrawing from the reaction medium of step (1), a gaseous productstream comprising cycloaliphatic hydrocarbon, hydrogen, and unreactedaromatic hydrocarbon starting material;

(3) reacting said gaseous product stream in the gaseous phase in contactwith a dry solid hydrogenating catalyst selected from the groupconsisting of nickel, cobalt, platinum, rhodium and ruthenium at about80-250 C. and about 1-100 atmospheres with the provision that a gaseousphase be maintained, thereby resulting in a highly pure gaseouscycloaliphatic hydrocarbon product substantially devoid of any aromatichydrocarbon impurities, and'further resulting in a process requiringneither external heat nor large equipment normally associated with gasphase reactions.

References Cited by the Examiner UNITED STATES iATENTS 2,952,625 9/60Kelley et a1. 208-216 2,979,546 4/61 Grandio et al. 260667 3,054,8339/62 Donaldson et a1 260-667 3,070,640 12/62 Pfeiifer et a1 260667 0ALPHONSO D. SULLIVAN, Primary Examiner.

1. A PROCESS FOR THE CATALYTIC, NON-DESTRUCTIVE HYDROGENATION OF ATLEAST ONE AROMATIC HYDROCARBON, WHICH PROCESS COMPRISES THE STEPS OF:(1) INTRODUCING SAID AROMATIC HYDROCARBON IN THE LIQUID STATE INTO THECORRESPONDING LIQUID CYCLOALIPHATIC HYDROCARBON CONTAINED IN A FIRSTREACTION ZONE, PASSING THROUGH SAID CYCLOALIPHATIC HYDROCARBON, ANAMOUNT OF GASEOUS HYDROGEN AT LEAST EQUAL TO THE STOICHIOMETRIC RATIOWITH RESPECT TO THE AROMATIC HYDROCARBON, SAID LIQUID CYCLOALIPHATICHYDROCARBON HAVING A GROUP VIII METAL HYDROGENATION CATALYST SUSPENDEDTHEREINTO, THE MOLAR RATIO BETWEEN SAID AROMATIC HYDROCARBON AND SAIDCYCLOALIPHATIC HYDROCARBON IN SAID FIRST REACTION ZONE BEING MAINTAINEDWITHIN THE RANGE OF FROM 0.003:1 TO 0.1:1, THE PRESSURE BEING COMPRISEDBETWEEN ABOUT 1 AND 100 ATMOSPHERES AND THE TEMPERATURE COMPRISEDBETWEEN 80 AND 250*C., PROVIDED THE TEMPERATURE IS AT LEAST 10*C. LOWERTHAN THE INITIAL BOILING TEMPERATURE OF SAID CYCLOALIPHATIC HYDROCARBONUNDER THE PREVAILING PRESSURE, AND (2) PASSING AS SUCH THE WHOLE,UNREACTED HYDROGENAND VAPORIZED HYDROCARBONS-CONTAINING GASEOUS PHASEISSUING FROM SAID FIRST REACTION ZONE THROUGH A BED OF A GROUP VIIIMETAL HYDROGENATION CATALYST IN A SECOND REACTION ZONE, AT A TEMPERATUREAND A PRESSURE IN THE SAME RANGE AS IN THE FIRST ZONE, PROVIDED THEY ARECONVENIENT TO MAINTAIN SAID UNREACTED HYDROGEN AND VAPORIZEDHYDROCARBONS IN THE GASEOUS STATE, THEREBY RESULTING IN A HIGHLY PUREGASEOUS CYCLOALIPHATIC HYDROCARBON PRODUCT SUBSTANTIALLY DEVOID OF ANYAROMATIC HYDROCARBON IMPURITIES, AND FURTHER RESULTING IN A PROCESSREQUIRING NEITHER EXTERNAL HEAT NOR LARGE EQUIPMENT NORMALLY ASSOCIATEDWITH GAS PHASE REACTIONS.